Augmented reality (AR) and mixed reality (MR) display systems allow a user to experience visual information presented from a computer simultaneously with ambient light from the user's surroundings. One method for allowing a user to view their surroundings while receiving additional visual information introduced in their field of view is an optical waveguide. A waveguide allows ambient light to reach a user's eyes, while also allowing light from a display device to be directed to the user's field of view and combined with the ambient light.
Directing the light from the display device through the waveguide to the user includes several optical elements, such as diffractive or holographic elements like in coupling and out coupling gratings. The optical performance of diffractive elements is sensitive to the geometry of, within and between, the gratings. Thermal expansion causing relative movement of or other changes to the gratings, therefore, can have a detrimental effect on the optical performance of a waveguide. Differential thermal expansion of the gratings can alter the intended optical performance of the image presented to the user.